feat(fs): resolve content URIs on Android (#1658)

* Implemented writeTextFile on Android.

* Added license headers.

* fix fmt checks.

* implement more file APIs

* change file

* cleanup

* refactor dialog plugin to leverage new FS APIs

* implement metadata functions

* fix build

* expose FS rust API

* resolve resources on android

* update pnpm

* update docs

---------

Co-authored-by: Lucas Nogueira <lucas@tauri.app>

plugins/fs/android/.gitignore

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+/build
+/.tauri

plugins/fs/android/build.gradle.kts

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+plugins {
+    id("com.android.library")
+    id("org.jetbrains.kotlin.android")
+}
+
+android {
+    namespace = "com.plugin.fs"
+    compileSdk = 34
+
+    defaultConfig {
+        minSdk = 21
+        targetSdk = 34
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+        consumerProguardFiles("consumer-rules.pro")
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
+    kotlinOptions {
+        jvmTarget = "1.8"
+    }
+}
+
+dependencies {
+
+    implementation("androidx.core:core-ktx:1.9.0")
+    implementation("androidx.appcompat:appcompat:1.6.0")
+    implementation("com.google.android.material:material:1.7.0")
+    testImplementation("junit:junit:4.13.2")
+    androidTestImplementation("androidx.test.ext:junit:1.1.5")
+    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")
+    implementation(project(":tauri-android"))
+}

plugins/fs/android/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

plugins/fs/android/settings.gradle

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+pluginManagement {
+    repositories {
+        mavenCentral()
+        gradlePluginPortal()
+        google()
+    }
+    resolutionStrategy {
+        eachPlugin {
+            switch (requested.id.id) {
+                case "com.android.library":
+                    useVersion("8.0.2")
+                    break
+                case "org.jetbrains.kotlin.android":
+                    useVersion("1.8.20")
+                    break
+            }
+        }
+    }
+}
+
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        mavenCentral()
+        google()
+
+    }
+}
+
+include ':tauri-android'
+project(':tauri-android').projectDir = new File('./.tauri/tauri-api')

plugins/fs/android/src/androidTest/java/ExampleInstrumentedTest.kt

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+// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+package com.plugin.fs
+
+import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.ext.junit.runners.AndroidJUnit4
+
+import org.junit.Test
+import org.junit.runner.RunWith
+
+import org.junit.Assert.*
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+@RunWith(AndroidJUnit4::class)
+class ExampleInstrumentedTest {
+    @Test
+    fun useAppContext() {
+        // Context of the app under test.
+        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
+        assertEquals("com.plugin.fs", appContext.packageName)
+    }
+}

plugins/fs/android/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+</manifest>

plugins/fs/android/src/main/java/FsPlugin.kt

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+// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+package com.plugin.fs
+
+import android.annotation.SuppressLint
+import android.app.Activity
+import android.content.res.AssetManager.ACCESS_BUFFER
+import android.net.Uri
+import android.os.ParcelFileDescriptor
+import app.tauri.annotation.Command
+import app.tauri.annotation.InvokeArg
+import app.tauri.annotation.TauriPlugin
+import app.tauri.plugin.Invoke
+import app.tauri.plugin.JSObject
+import app.tauri.plugin.Plugin
+import java.io.File
+import java.io.FileOutputStream
+import java.io.IOException
+import java.io.InputStream
+import java.io.OutputStream
+
+@InvokeArg
+class WriteTextFileArgs {
+  val uri: String = ""
+  val content: String = ""
+}
+
+@InvokeArg
+class GetFileDescriptorArgs {
+    lateinit var uri: String
+    lateinit var mode: String
+}
+
+@TauriPlugin
+class FsPlugin(private val activity: Activity): Plugin(activity) {
+    @SuppressLint("Recycle")
+    @Command
+    fun getFileDescriptor(invoke: Invoke) {
+        val args = invoke.parseArgs(GetFileDescriptorArgs::class.java)
+
+        val res = JSObject()
+
+        if (args.uri.startsWith(app.tauri.TAURI_ASSETS_DIRECTORY_URI)) {
+            val path = args.uri.substring(app.tauri.TAURI_ASSETS_DIRECTORY_URI.length)
+            try {
+                val fd = activity.assets.openFd(path).parcelFileDescriptor?.detachFd()
+                res.put("fd", fd)
+            } catch (e: IOException) {
+                // if the asset is compressed, we cannot open a file descriptor directly
+                // so we copy it to the cache and get a fd from there
+                // this is a lot faster than serializing the file and sending it as invoke response
+                // because on the Rust side we can leverage the custom protocol IPC and read the file directly
+                val cacheFile = File(activity.cacheDir, "_assets/$path")
+                cacheFile.parentFile?.mkdirs()
+                copyAsset(path, cacheFile)
+
+                val fd = ParcelFileDescriptor.open(cacheFile, ParcelFileDescriptor.parseMode(args.mode)).detachFd()
+                res.put("fd", fd)
+            }
+        } else {
+            val fd = activity.contentResolver.openAssetFileDescriptor(
+                Uri.parse(args.uri),
+                args.mode
+            )?.parcelFileDescriptor?.detachFd()
+            res.put("fd", fd)
+        }
+
+        invoke.resolve(res)
+    }
+
+    @Throws(IOException::class)
+    private fun copy(input: InputStream, output: OutputStream) {
+        val buf = ByteArray(1024)
+        var len: Int
+        while ((input.read(buf).also { len = it }) > 0) {
+            output.write(buf, 0, len)
+        }
+    }
+
+    @Throws(IOException::class)
+    private fun copyAsset(assetPath: String, cacheFile: File) {
+        val input = activity.assets.open(assetPath, ACCESS_BUFFER)
+        input.use { i ->
+            val output = FileOutputStream(cacheFile, false)
+            output.use { o ->
+                copy(i, o)
+            }
+        }
+    }
+}
+

plugins/fs/android/src/test/java/ExampleUnitTest.kt

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+// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+package com.plugin.fs
+
+import org.junit.Test
+
+import org.junit.Assert.*
+
+/**
+ * Example local unit test, which will execute on the development machine (host).
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+class ExampleUnitTest {
+    @Test
+    fun addition_isCorrect() {
+        assertEquals(4, 2 + 2)
+    }
+}